RNA polymerases I and III are being purified to allow comparison of their respective sub-unit structures. Accessory proteins (pi-factor) which stimulate polymerase III have been purified to homogeneity. Several of these proteins bind to DNA. Competitive filter-binding experiments are in progress to measure the degree of preference of these proteins for binding to yeast DNA rather than calf thymus or phage T7 DNA. Within the next year, in vitro transcription experiments will shift toward the study of simple, well-defined and intact double- stranded DNA templates. The ability of diploid yeast cells to undergo meiosis and form spores is normally controlled by the active alleles at the mating type region present in the diploid. Normally, only diploid cells containing one a and one alpha type region can undergo sporulation. Physiological studies indicate that cells lacking the a/alpha genetic constitution fail to carry out a number of the biochemical processes that accompany sporulation. In order to learn how mating type genes control sporulation, we have isolated constitutive mutants, able to sporulate in alpha/alpha background. Physiological characterization, allelism tests, and genetic mapping will be carried out with these mutants.